/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* $Id: ServletContextURIResolver.java 679326 2008-07-24 09:35:34Z vhennebert $ */
package org.apache.fop.servlet;

import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;

import javax.servlet.ServletContext;
import javax.xml.transform.Source;
import javax.xml.transform.TransformerException;
import javax.xml.transform.URIResolver;
import javax.xml.transform.stream.StreamSource;

/**
 * This class is a URIResolver implementation that provides access to resources
 * in the WEB-INF directory of a web application using "servlet-content:" URIs.
 */
public class ServletContextURIResolver implements URIResolver {

	/**
	 * The protocol name for the servlet context URIs.
	 */
	public static final String SERVLET_CONTEXT_PROTOCOL = "servlet-context:";
	private ServletContext servletContext;

	/**
	 * Main constructor
	 *
	 * @param servletContext the servlet context to access the resources
	 * through
	 */
	public ServletContextURIResolver(ServletContext servletContext) {
		this.servletContext = servletContext;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public Source resolve(String href, String base) throws TransformerException {
		if (href.startsWith(SERVLET_CONTEXT_PROTOCOL)) {
			return resolveServletContextURI(href.substring(SERVLET_CONTEXT_PROTOCOL.length()));
		} else {
			if (base != null && base.startsWith(SERVLET_CONTEXT_PROTOCOL) && (href.indexOf(':') < 0)) {
				String abs = base + href;
				return resolveServletContextURI(abs.substring(SERVLET_CONTEXT_PROTOCOL.length()));
			} else {
				return null;
			}
		}
	}

	/**
	 * Resolves the "servlet-context:" URI.
	 *
	 * @param path the path part after the protocol (should start with a
	 * "/")
	 * @return the resolved Source or null if the resource was not found
	 * @throws TransformerException if no URL can be constructed from the
	 * path
	 */
	protected Source resolveServletContextURI(String path) throws TransformerException {
		while (path.startsWith("//")) {
			path = path.substring(1);
		}
		try {
			URL url = this.servletContext.getResource(path);
			InputStream in = this.servletContext.getResourceAsStream(path);
			if (in != null) {
				if (url != null) {
					return new StreamSource(in, url.toExternalForm());
				} else {
					return new StreamSource(in);
				}
			} else {
				throw new TransformerException("Resource does not exist. \"" + path + "\" is not accessible through the servlet context.");
			}
		} catch (MalformedURLException mfue) {
			throw new TransformerException("Error accessing resource using servlet context: " + path, mfue);
		}
	}
}